Communication system using geographic position data

ABSTRACT

A wireless communication system employs directive antenna arrays and knowledge of position of users to form narrow antenna beams to and from desired users and away from undesired users to reduce co-channel interference. By reducing co-channel interference coming from different directions, spatial filtering with antenna arrays improves the call capacity of the system. A space division multiple access (SDMA) system allocates a narrow antenna beam pattern to each user in the system so that each user has its own communication channel free from co-channel interference. The position of the users is determined using geo-location techniques. Geo-location can be derived via triangulation between cellular base stations or via a global positioning system (GPS) receiver. The system can be optimized by applying partially adaptive processing algorithms, which are seeded by geo-location data.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.09/188,835, filed on Nov. 9, 1998, which is a continuation ofInternational Application Number PCT/US97/18780, filed on Oct. 10, 1997,Publication No. WO98/16077, which is a continuation-in-part of U.S. Ser.No. 08/729,289, filed on October 10, 1996, now U.S. Pat. No. 6,512,481,issued Jan. 28, 2003, the entire teachings of which are bothincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] At present, the communications spectrum is at a premium, withprojected high capacity requirements of Personal Communication Systems(PCS) adding to the problem. Although all modulation techniques forwireless communications suffer capacity limitations due to co-channelinterference, spread spectrum, or Code Division Multiple Access (CDMA),is a modulation technique which is particularly suited to take advantageof spatial processing to increase user capacity. Spread spectrumincreases signal bandwidth from R (bits/sec) to W (Hz), where W>>R, somultiple signals can share the same frequency spectrum. Because theyshare the same spectrum, all users are considered to be co-channelinterferers. Capacity is inversely proportional to interference power,so reducing the interference increases the capacity.

[0003] Some rudimentary spatial processing can be used to reduceinterference, such as using sector antennas. Instead of using a singleomnidirectional antenna, three antennas each with a 120 degree sectorcan be used to effectively reduce the interference by three, because, onaverage, each antenna will only be looking at ⅓ of the users. Byrepeating the communications hardware for each antenna, the capacity istripled.

[0004] Ideally, adaptive antenna arrays can be used to effectivelyeliminate interference from other users. Assuming infinitesimalbeamwidth and perfect tracing, adaptive array processing (AAP) canprovide a unique, interference-free channel for each user. This exampleof space division multiple access (SDMA) allows every user in the systemto communicate at the same time using the same frequency channel. Suchan AAP SDMA system is impractical, however, because it requiresinfinitely many antennas and complex signal processing hardware.However, large numbers of antennas and infinitesimal beamwidths are notnecessary to realize the practical benefits of SDMA.

[0005] SMDA allows more users to communicate at the same time with thesame frequency because they are spatially separated. SDMA is directlyapplicable to a CDMA system. It is also applicable to a time divisionmultiple access (TDMA) system, but to take full advantage of SDMA, thisrequires monitoring and reassignment of time-slots to allow spatiallyseparated users to share the same time-slot simultaneously. SDMA is alsoapplicable to a frequency division multiple access (FDMA) system, butsimilarly, to take full advantage of SDMA, this requires monitoring andreassignment of frequency-slots to allow spatially separated users toshare the same frequency band at the same time.

[0006] In a cellular application, SDMA directly improves frequencyre-use (the ability to use the same frequency spectrum in adjoiningcells) in all three modulation schemes by reducing co-channelinterference between adjacent cells. SDMA can be directly applied to theTDMA and FDMA modulation schemes even without re-assigning time orfrequency slots to null co-channel interferers from nearby cells, butthe capacity improvement is not as dramatic as if the time and frequencyslots are re-assigned to take full advantage of SDMA.

SUMMARY OF THE INVENTION

[0007] Instead of using a fully adaptive implementation of SDMA,exploitation of information on users' position changes the antennabeamforming from an adaptive problem to deterministic one, therebysimplifying processing complexity. Preferably, a beamformer uses asimple beam steering calculation based on position data. Smart antennabeamforming using geo-location significantly increases the capacity ofsimultaneous users, but without the cost and hardware complexity of anadaptive implementation. In a cellular application of the invention,using an antenna array at the base station (with a beamwidth of 30degrees for example) yields an order of magnitude improvement in callcapacity by reducing interference to and from other mobile units. Usingan antenna array at the mobile unit can improve capacity by reducinginterference to and from other cells (i.e., improving frequency reuse).For beamforming, the accuracy of the position estimates for each mobileuser and update rates necessary to track the mobile users are wellwithin the capabilities of small, inexpensive Global Positioning System(GPS) receivers.

[0008] In general, the present invention is a communication system witha plurality of users communicating via a wireless link. A preferredembodiment of the invention is a cellular mobile telephone system. Eachuser has a transmitter, receiver, an array of antennas separated inspace, a device and method to determine its current location, hardwareto decode and store other users' positions, and beamformer hardware. Thebeamformer uses the stored position information to optimally combine thesignals to and from the antennas such that the resulting beam pattern isdirected toward desired users and away from undesired users.

[0009] An aspect of the invention uses a deterministic direction findingsystem. That system uses geo-location data to compute an angle ofarrival for a wireless signal. In addition, the geo-location data isused to compute a range for the wireless signal. By using the determinedangel of arrival and range, a system in accordance with the inventioncan deterministically modify the wireless signal beam betweentransceivers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The foregoing and other objects, features and advantages of theinvention, including various novel details of construction andcombination of parts will be apparent from the following more particulardrawings and description of preferred embodiments of the communicationsystem using geographic position data in which like referencescharacters refer to the same parts throughout the different views. Itwill be understood that the particular apparatus and methods embodyingthe invention are shown by way of illustration only and not as alimitation of the invention, emphasis instead of being placed uponillustrating the principles of the invention. The principles andfeatures of this invention may be employed in various and numerousembodiments without departing from the scope of the invention.

[0011]FIG. 1 is a schematic diagram of a cellular communication system.

[0012]FIG. 2 is a schematic block diagram of components in a basestation and a mobile unit of FIG. 1.

[0013]FIG. 3 is a schematic diagram of a general adaptive antenna array.

[0014]FIG. 4 is a schematic diagram of a mobile-to-base communicationslink in cellular communications using AAP SDMA.

[0015]FIG. 5 is a schematic diagram of a base-to-mobile communicationslink in cellular communications using AAP SDMA.

[0016]FIG. 6 is a schematic diagram of a general SDMA communicationssystem employing geo-location techniques.

[0017]FIG. 7 is a schematic block diagram of two communicating users ofFIG. 6.

[0018]FIG. 8 is a flow chart of a method of operating a cellulartelephone system using geo-location data.

[0019]FIG. 9 is a schematic diagram of a cellular telephone system usinggeo-location data.

[0020]FIG. 10 is a schematic block diagram of a steering circuit.

[0021]FIG. 11 is a schematic block diagram of a nulling circuit.

[0022]FIG. 12 is a schematic block diagram of a receiver module for amobile unit beamformer.

[0023]FIG. 13 is a schematic block diagram of a transmitter module for amobile unit beamformer.

[0024]FIG. 14 is a schematic block diagram of a receiver module for abase station beamformer.

[0025]FIG. 15 is a schematic block diagram of a transmitter module for abase station beamformer.

[0026]FIG. 16 is a schematic block diagram of a preferred base stationemploying real-valued FIR filtering at IF.

[0027]FIG. 17 is a schematic block diagram of a preferred base stationemploying complex-valued FIR filtering at base band.

[0028]FIG. 18 is a schematic block diagram of a beamshaping circuitbased on an adaptive-array processing algorithms.

DETAILED DESCRIPTION OF THE INVENTION

[0029]FIG. 1 is a schematic diagram of a general land-based cellularwireless communications system. The geographic area serviced by thiscommunications system 1 is divided into a plurality of geographic cells10, each cell 10 having a respective geographically fixed base station20. Each cell 10 can have an arbitrary number of mobile cellular units30, which can travel between and among the cells 10.

[0030]FIG. 2 is a schematic block diagram of components in a basestation 20 and a mobile unit 30 of FIG. 1. As shown, each base station20 includes a transceiver 210 having a transmitter 212 and a receiver214, control hardware 220, and a set of antennas 25 to communicate witha plurality of mobile units 30. The mobile units are free to roam aroundthe entire geographic service area. Each mobile unit 30 includes atransceiver 310 having a transmitter 312 and a receiver 314, controlhardware 320, a handset 8, and an antenna or antennas 35 to allow forsimultaneous sending and receiving of voice messages to the base station20. The base station 20 communicates with a mobile telecommunicationsswitching office (MTSO) 5 to route the calls to their properdestinations 2.

[0031] The capacity of a spread spectrum cellular communication systemcan be expressed as:

N=(W/R)(N _(O) /E _(b))(1/D)F G   (1)

[0032] where W is the bandwidth (typically 1.25 MHz);

[0033] R is the data rate (typically 9600 bps);

[0034] E_(b)/N_(O) is the energy-to-noise ratio (typically 6 dB);

[0035] D is the voice duty-cycle (assumed to be 0.5);

[0036] F is the frequency reuse (assumed to be 0.6);

[0037] G is the number of sectors per cell (assumed to be 1, oromnidirectional); and

[0038] N is the number of simultaneous users.

[0039] As such, a typical cell can support only about 25-30 simultaneouscalls. Space division multiple access (SDMA) techniques can be used toincrease capacity.

[0040] The capacity improvement by using an adaptive array at the basestation 20 in the mobile-base link is summarized below in Table I. Theresults are valid for various antenna beamwidths at a fixed outageprobability of 10⁻³. TABLE I Base Station Antenna Beamwidth vs. CallCapability in Mobile-to-Base Link Beamwidth (degrees) Capacity(calls/cell) 360 (omni) 31 120 75  60 160  30 320

[0041]FIG. 3 is schematic diagram of an M-element adaptive antenna array35 a, 35 b, 35 c and beamformer 54. Each element has N adaptive linearfilters (ALFs) 55, where N is the number of users per cell. Each of theALFs 55 are adapted in real time to form a beam to and from each mobileunit 30 via a combiner 57. The ALFs 55 use a variety of techniques toform an optimal beam, such as using training sequences, dynamicfeedback, and property restoral algorithms. Preferably, the ALFs 55 aresingle chip adaptive filters as described in U.S. Pat. No. 5,535,150 toChiang, the teachings of which are incorporated herein by reference.

[0042] The M-element array is capable of nulling out M−1 co-channelinterference sources. However, all the users in a CDMA cell share thesame frequency band and therefore, are all co-channel interferers in themobile-to-base link. Because the number of users, N, far exceeds thenumber of antennas, M, subspace methods of direction-of-arrivalestimation are not applicable. Instead, a Constant Modulus Algorithm(CMA) adaptive beamforming approach is more applicable.

[0043] For the base-to-mobile link, the co-channel interferers are theneighboring base stations. Conceivably, the number of antennas in theadaptive array at the mobile could be approximately the same as thenumber of neighboring base stations, so subspace methods ofdirection-of-arrival estimation may be applicable to null out theinterfering base stations. The computational complexity of both types ofAAP algorithms is approximately equal.

[0044] The majority of the computational complexity incurred by usingAAP in a cellular system is due to covariance formulation and copyprocessing. The covariance is a sum of a sequence of matrices, each ofwhich is an outer product of complex array samples. Each term of thisouter product is a complex product. The computation requires on theorder of K² computations, where K is the number of antennas. Using thecovariance, the AAP algorithm computes the antenna weight vector, whichis applied to the received signal vectors. This is a matrix inversion,which copies the desired signal. The covariance is updated periodically,and each desired signal is copied in real time.

[0045] Overall about ½ to ⅔ of the computational complexity incurred byusing AAP SDMA in a cellular system is due to the covariance formulationalone, and the remaining complexity resides in the matrix inversion forcopy weight generation. The complexity, size, power consumption, andcost of implementing AAP SDMA has thus far prevented it from gainingacceptance. In preferred embodiments, the present invention achievessubstantially the same results as a fully adaptive implementation ofSDMA but with significantly less hardware complexity, smaller size,lower power consumption, and lower cost.

[0046]FIG. 4 is a schematic diagram of a mobile-to-base communicationlink in a cellular communications system using AAP SDMA. Illustrated arethe antenna array SDMA transmission beam patterns 150 from the mobileunits 30 to the base station 20 along a central direction 155. Alsoillustrated is interference 170 which would exist without SDMA.

[0047] Assuming the base station 20 employs a multi-antenna adaptivearray while the mobile unit 30 uses a single omnidirectional antenna, inthe reverse channel (uplink, or mobile-to-base), the base station arrayreduces interference from other users both in-cell and out-of-cell, asillustrated in FIG. 4, by pointing its reception beam only towards thedesired mobile unit 30.

[0048] For a 120 degree beamwidth, about ⅓ of the mobile units 30 in acell 10 are visible to the array, so the capacity is approximatelytripled. Similarly, for a 30 degree beamwidth, about {fraction (1/12)}of the mobile units 30 in a cell 10 are visible to the array, so thecapacity is increased by a factor of approximately 12.

[0049] Assuming that both the base station 20 and the mobile unit 30employ multi-element antenna arrays, for the reverse channel, thissystem significantly reduces interference from out-of-cell mobiletransmitters, because they are forming beams toward their own basestation 20. Ideally, this would improve the frequency reuse, F, from 0.6to nearly 1.0, thereby increasing the capacity by nearly ⅔. Simulationson such a system show that a frequency re-use factor of F=0.8826 with a60 degree beamwidth from the mobile unit improves capacity by 47% overthe omnidirectional case (F=0.6).

[0050] Improvement due to adaptive arrays on the mobile units 30 are notas dramatic as those achieved with adaptive arrays at the base station20. In addition, complexity, size, power, and cost can make theapplication of antenna arrays in mobile units 30 impractical for mostsituations. The reduction in inter-cell interference afforded byadaptive arrays in mobile units 30 may, however, be critical inhigh-traffic environments and for mobile units 30 near the cellboundaries where interference is the greatest.

[0051]FIG. 5 is a schematic diagram of a base-to-mobile communicationlink in a cellular communications system using AAP SDMA. Assuming thebase station 20 employs a multi-antenna array while the mobile unit 30uses a single omnidirectional antenna, in the base-to-mobile link, thebase station 20 antenna array reduces interference to other users bothin-cell 180 and out-of-cell 175, as illustrated in FIG. 4. Results forthis channel for various beamwidths are summarized below in Table II.TABLE II Base Station Antenna Beamwidth vs. Call Capacity inBase-to-Mobile Channel Beamwidth (degrees) Capacity (calls/cell) 360(omni) 30  75 (5 antennas) 120  55 (7 antennas) 165

[0052] Assuming that both the base station 20 and the mobile units 30employ multi-element adaptive antenna arrays, for the forward channel,this system significantly reduces interference from out-of-cell basestations, because the mobile units 30 are forming beams toward their ownbase station 20. As in the reverse channel, ideally, this would improvethe frequency re-use, F, from 0.6 to nearly 1.0, thereby increasing thecapacity by nearly ⅔.

[0053]FIG. 6 is a schematic diagram of a general SDMA communicationssystem employing geo-location techniques. As illustrated, a first user301 and a second user 302 are in communication. The first user 301computes the direction of the desired user 302 and a beam pattern 314 isformed along the desired direction 316. In addition to desired users302, the first user 301 wants to avoid projecting a beam in thedirection 317 of an undesired user 303. Furthermore, the first user 301wants to avoid receiving a beam from any direction other than thedesired direction 316. These goals are accomplished by utilizing anarrow directional radio beam.

[0054] The radio-beam extends from the transmitting unit at a beamwidthangle B_(o). The distance from the transmitting unit to the receivingunit is designated as r_(m). The beamwidth at the receiving unit isB_(m). In a cellular system, a base unit is located at the center of ageographical cell of radius R and the receiving unit is generally mobileand moves with a velocity V.

[0055]FIG. 7 is a schematic block diagram of communicating users of FIG.6. As illustrated, the first user 301 and the second user 302 receivegeo-location data from a satellite system 90. The users 301, 302communicate using a respective antenna array 52 controlled by arespective beamformer circuit 34. In addition to the standardtransceiver 310 and control hardware 320, a Global Positioning System(GPS) circuit 350 communicates with a global positioning satellitesystem 90 to command the beamformer 34. Although a satellite system 90is illustrated, the geo-location data can be provided by or derived froma ground-based positioning system. Furthermore, a differential globalpositioning system using both ground and satellite based transmitterscan be employed to provide a higher resolution location.

[0056]FIG. 8 is a flow chart of a method of operating a cellulartelephone system using geo-location data. As a part of the initialestablishment of the wireless link (step 500) between the mobile unit 30and the base station 20, the mobile unit 30 must determine its currentposition. The GPS receiver may not already be tracking satellites andcould take several minutes to get an accurate position estimate (coldstart). If the GPS receiver 350 is cold starting (step 510), the basestation 20 provides a rough location estimate to orient the GPS receiverand significantly expedite the position acquisition (step 512). It cansend an estimate of the mobile unit's location via triangularizationfrom adjacent base stations. This information can be sent along with aChannel Assignment Message (which informs the mobile unit of a TrafficChannel on which to send voice and data) via a Paging Channel. Usersshare the Paging Channel to communicate information necessary for theestablishment of calls.

[0057] Then the base station 20 transmits its position to the mobileunit 30 via the Paging Channel (Step 520). If the mobile unit 30 isemploying a directive antenna array 35′, it uses the base stationposition and its current position and heading information to form a beampattern toward the base station 20 as described above (step 530). Themobile tunes to the Traffic Channel and starts sending a Traffic Channelpreamble and the current mobile location information to the base stationvia a Reverse Traffic Channel (step 540). Every two seconds, the GPSlocation is updated and sent to the base station via the Reverse TrafficChannel.

[0058] If the mobile unit 30 is employing a directive antenna array 35′,every two seconds it uses the current heading information and comparesits updated position information to the stored location of the currentbase station to update the beam pattern toward the base station. Also,the base station 20 receives the updated mobile unit locationinformation and updates its beam pattern toward the mobile unit (step550). During hand-off between base stations (step 560), the directivityof the mobile antenna array, if employed, is disabled (step 570) toallow the user to communicate with other base stations.

[0059]FIG. 9 is a schematic diagram of a cellular telephone system usinggeo-location data. A preferred embodiment is an implementation of SDMAusing knowledge of user position in a cellular spread spectrumcommunication system. Fixed base stations 20 communicate with rovingmobile units 30 within a prescribed geographic cell 10. Each basestation 20 consists of a transceiver 210, a directional antenna array25′ and associated beamformer hardware 24, control hardware 220, and atransmission link with a mobile telecommunications switching office(MTSO) 5 to route calls. The mobile unit 30 consists of handset 8 with amicrophone and a speaker, a transceiver 310, a GPS receiver 350 (orother hardware to determine position of the mobile), and anomnidirectional antenna 35 or optionally a directional antenna array 35′and associated beamformer hardware 34.

[0060] A preferred embodiment of the invention employs a conventionalCDMA base station but with the addition of a 10-element directionalantenna array 25′ capable of forming antenna patterns with a beamwidthof 36 degrees, beamformer hardware 24, and additional modems toaccommodate the order of magnitude increase in call capacity. Thebeamformer hardware 24 takes as input the current latitude and longitudeof each mobile unit, compares it with the known location of the basestation 20 to determine the angle of arrival (AOA) of each mobile unit'ssignal, and generates a set of complex antenna weights to apply to eachantenna output for each mobile unit such that the combined signalrepresents a beam pattern steered in the direction of the desired mobileunit for both the transmit and receive signals. The complex antennaweights are calculated to simply steer the antenna beam.

[0061] Instead of calculating the weights in real-time, a set of weightscan be stored in a Programmable Read-Only Memory (PROM) for a finite setof angles of arrival, and can be recalled and immediately applied. Thebeam pattern is preferably widened as the mobile unit 30 approaches thebase station 20 (as described below) because the beam coverage decreasesas the mobile unit 30 approaches the base station 20. Furthermore, theassumption that multipath components propagate from approximately thesame location as the mobile unit 30 becomes less valid as the mobileunit 30 approaches the base station. Optionally, the beamformer hardware24 can track multiple mobile units simultaneously and place nulls oninterfering mobile units, but this is more computationally complex(although not as complex as a fully adaptive array).

[0062] The base station antenna array forms an antenna pattern withbeamwidth B₀=30 degrees. Assuming the cell radius is R=6 km, the mobileunit is at radius r_(m) (m), the maximum velocity of the mobile unit isV=100 (km/h), and the location estimate is updated at U=2 times persecond, examination of the pie-slice geometry of the antenna patternreveals that the antenna beam width at the mobile unit's location isB_(m)=2πr_(m) (B₀/360) meters, which decreases as the mobile unit 30approaches the base station 20. Once a location estimate has beendetermined for the mobile unit 30 and transmitted to the base station20, the base station 20 forms an antenna pattern with the main lobecentered on the mobile unit 30.

[0063] In the worst case, this estimate is wrong by T=30 m. In an updatecycle, the mobile travels V/U (m), and as long as this distance is lessthan B_(m)/2 (half the beamwidth in meters at the mobile location) minusthe error in the location estimate, T, then the mobile will remainwithin the antenna main lobe: V/U≦(B_(m)/2)−T . Evaluating this equationwith the typical numerical values and solving for the mobile locationyields r_(m)≧167.6 m at a velocity V=100 km/h. Therefore the mobile unit30 remains in the beam coverage area as long as it is further than 167.6m from the base station 20.

[0064] The base station 20 uses the location information to sense whenthe mobile unit 30 is closer than 167.6 m and widens the beam pattern toomnidirectional (or optionally to 120 degrees). The widening does notsignificantly increase interference to other users because the low poweris used for nearby mobile units 30. The complex antenna weights for thewidened beams are preferably stored in memory for a finite set of anglesof arrival, and they can be recalled and immediately applied.

[0065] The mobile units 30 include a conventional handset 8 preferablyaugmented with an integrated GPS receiver 350 and modifications to thecontrol logic 320 to incorporate the GPS position data in thetransmission to the base station 20. Mobile units 30 embodied inautomobiles preferably employ a three-element directional antenna array35′ mounted on the automobile and beamformer hardware 34 in addition tothe handset with the build-in GPS receiver as described above. Thebeamformer hardware 34 stores the current base station's latitude andlongitude, compares it with its own current latitude and longitude, andcomputes its current heading via GPS doppler in information to determinethe angle of the arrival of the base station signal. A look-up table(for example in a ROM) provides the antenna weights to steer thetransmit and receive beam pattern toward the base station. Optionallythe beamformer hardware can track multiple base stations simultaneouslyand place nulls on interfering base stations.

[0066] The necessary accuracy of the mobile position determinationdepends on the width of the antenna beam. Assuming the location can bedetermined to within a tolerance of T=30 m (i.e., the location can bedetermined with high probability to be within a circle of radius T=30m), as the mobile unit 30 moves, the antenna beam must cover the entirearea in which the mobile unit 30 can move in the two seconds before theposition is checked again and the antenna beam pattern is updated.Because of the pie-slice geometry of the beam pattern, as the mobileunit 30 approaches the base station 20, the beam coverage decreases andmust be widened to cover the area in which the mobile unit 30 couldtravel in the two second update cycle.

[0067] Mobile units employing the antenna array 35′ can form an antennapattern with beamwidth B₁=120 degrees. Assuming the cell radius is R=6km, the mobile is at radius r_(m) (meters), the maximum rotation of themobile unit is Ω=45 degrees/second (i.e., the mobile can turn a 90degree corner in 2 seconds), and the location estimate is updated at U=2times per second, examination of the pie-slice geometry of the antennapattern yields a location tolerance at the base station ofT_(b)=360T/(2πr_(m)) (degrees), which increases as the mobile unit 30approaches the base station 20.

[0068] In addition to location, the mobile unit 30 needs to know itsdirection of travel so it can determine the orientation of its antennaarray. This direction vector can be deduced from GPS doppler data orfrom a compass.

[0069] Once a location estimate has been determined, the mobile unit 30forms an antenna pattern with the main lobe centered on the base station20. In the worse case, this estimate is wrong by T_(b) (degrees) and themobile unit 30 is turning at maximum rotation Ω=45 degrees/s. In anupdate cycle, the mobile's main lobe rotates Ω/U (degrees), and as longas this angle is less than B₁/2 (half the mobile beamwidth in degrees)minus the error in the location estimate, T_(b) (degrees), then the basestation 20 will remain within the mobile antenna's main lobe, Ω/U≦(B₁/2)−T_(b). Evaluating this equation with the numerical values aboveand solving for the mobile location yields r_(m)≧45 m . Therefore thebase station 20 remains in the beam coverage area as long as it isfurther than 45 m from the mobile unit 30.

[0070] The mobile unit 30 uses its location information to sense when itis closer than 45 m to the base station 20 and widens the beam patternto omnidirectional. Again, this widening does not significantly increaseinterference to other users because the power transmitted is low. Alook-up table in a ROM provides the antenna weights to change the beampattern to omnidirectional when the mobile unit 30 is within 45 m of thebeam station or during call hand-ff when the mobile unit 30 iscommunicating with more than one base station 20.

[0071] A preferred embodiment of the invention includes an aspect whichreduces interference and improves capacity as long as the multipathcomponents propagate from approximately the same direction as theline-of-sight (LOS) component, which is a fair assumption. Typically, amultipath signal is limited to a 5-10° arc relative to the receiver. Assuch, various techniques can be employed to identify and null themultipath component of a received signal.

[0072] Aspects of the invention can be practiced even if some users arenot equipped with SDMA capability. In the case that a particular userdoes not employ an antenna array, the user will not use positioninformation and will default to conventional omnidirectionaltransmission and/or reception. Similarly, in the case that the user doesnot provide position information, other users will default toconventional omnidirectional transmission to and/or reception from thatuser. As conventional users are phased out and SDMA equipped users arephased in, the capacity of the system will increase as the fraction ofSDMA equipped users increases.

[0073]FIG. 10 is a schematic block diagram of a steering circuit. Thesteering circuit 52 includes a GPS receiver 522 connected to a GPSantenna 520 for receiving GPS signals from satellites. The GPS receiver522 computes the unit's latitude and longitude. A deterministicdirection finder 524 processes the mobile unit latitude LAT_(M) andlongitude LNG_(M) data as well as the base station latitude LAT_(B) andlongitude LNG_(B) data using a first look-up table to compute an angleof arrival (AOA) and a range (RNG) based on the following equations:$\begin{matrix}{{AOA} = {\tan^{- 1}( \frac{{LNG}_{M} - {LNG}_{B}}{{LAT}_{M} - {LAT}_{B}} )}} & (2) \\{{RNG} = \sqrt{( {{LAT}_{M} - {LAT}_{B}} )^{2} + ( {{LNG}_{M} - {LNG}_{B}} )^{2}}} & (3)\end{matrix}$

[0074] The AOA and RNG values are processed by a second look-up table inan antenna steering unit 526 which converts the values into antennaweights. The antenna weights are calculated to steer the beam in thedirection of the angle of arrival. That is, the antenna weights unity(i.e., omnidirectional) when the range is below a prescribed threshold(i.e., the mobile unit is very close to the base station) and for themobile unit during handoff. The antenna weights are provided to thebeamformer.

[0075]FIG. 11 is a schematic block diagram of a nulling circuit.Position data from each user is processed by a GPS circuit 521 _(a), . .. ,521 _(k). For a particular user “a”, a desired latitude LAT_(Ma) andlongitude LNG_(Ma) data are received and for other users undesirablelatitude LAT_(Mb), . . . ,LAT_(Mk) and longitude LNG_(Mb), . . .,LNG_(Mk) data are received. A first look-up table in a deterministicdirection finder unit 523 converts the latitude and longitude data fromthe mobile units into desired AOA_(a) and undesired AOA_(b), . . .,AOA_(k) angles of arrival and a desired range RNG based on the basestation latitude LAT_(B) and longitude LNG_(B) data. This informationfor each user is passed to a second look-up table in a nulling unit 525which computes antenna weights which are calculated to steer the beam inthe direction of the desired angle of arrival AOA_(a) and away from theundesired angle of arrivals AOA_(b), . . . ,AOA_(k) (i.e., a circuitnulls undesired users). The antenna weights can become unity asdescribed above. The antenna weights from the nulling unit 525 areprovided to the beamformer.

[0076]FIG. 12 is a schematic block diagram of a receiver module for amobile unit beamformer. The circuit receives a plurality of RF signalsIN_(a), IN_(b), IN_(c) over a respective antenna 35′a, 35 ′b, 36′c of adirectional antenna array 35′. The RF signals are processed into threebaseband signal channels by a three-channel receiver 312. Each basebandsignal is processed by a programmable filter 342 a, 342 b, 342 c. A GPSsignal from a GPS receiver (not shown) is received by a steering/nullingcircuit 344 operating as described above. The steering/nulling circuit344 controls the programmable filters 342 a, 342 b, 342 c. The outputsfrom the programmable filters are combined by a RF combiner 346 toproduce an output signal OUT.

[0077]FIG. 13 is a schematic block diagram of a transmitter module for amobile unit beamformer. The input signal IN is split three ways andprocessed by respective programmable filters 341 a, 341 b, 341 c. Theprogrammable filters 341 are controlled by a steering/nulling circuit343 based on inputs from a GPS receiver (not shown) as described above.Three channels of baseband signals result from the programmable filtersand are fed to a three-channel transmitter 314 which sends RF signalsOUT_(a), OUT_(b), OUT_(c) to a respective antenna 35′a, 35 b, 35 ′c inthe antenna array 35′. In a preferred embodiment of the invention, thesystem implements programmable filtering by including a vector-matrixproduct processing system as described in U.S. Pat. No. 5,089,983 toChiang, the teachings of which are incorporated herein by reference.

[0078]FIG. 14 is a schematic block diagram of a receiver module for abase station beamformer. As illustrated, the antenna array 25′ of thebase station includes 10 antennas 25′₁, . . . ,25′₁₀. The input signalsIN₁, . . . ,IN₁₀ are received by a ten-channel receiver 212 which yieldsten channels of baseband signals. Each channel of baseband signal isprocessed by a programmable filter array 242, each of which includes arespective programmable filter for each of N possible users. Theprogrammable filters 242 are controlled by a steering/nulling circuit244 for each user based on GPS data received from each user as describedabove. The outputs from the programmable filters 242 are combined by anRF combiner 246 into N outputs OUT.

[0079]FIG. 15 is a schematic block diagram of a transmitter module for abase station beamformer. The transmitter section receives an inputsignal IN which is split ten ways into ten channels. Each channel isprocessed by a programmable filter array 241 having a programmablefilter for each N possible users. The programmable filters arecontrolled by a steering/nulling circuit 243 for each user based on GPSdata from each mobile user as described above. The programmable filtersyield N baseband signals divided into ten channels which are transmittedto the antenna array 25′ by a ten-channel transmitter 214. Each antenna25′₁, . . . ,25′₁₀ receives a respective RF output signal OUT₁, . . .,OUT₁₀ from the transmitter 214.

[0080] In a preferred embodiment of the invention, a cellular basestation includes sufficient signal-processing hardware to support theuse of geo-location information, received from mobile transmitters, tooptimally shape the receiving antenna-array pattern. This approach is analternative to using a fully adaptive antenna-array that requires asignificantly greater cost in terms of hardware and software.

[0081] To implement a fully-adaptive base station receiver, an array ofantenna inputs must be processed to yield a set of complex-valuedweights that are fed back to regulate the gain and phase of the incomingsignals. The need for multiple weights applied to a single input signalimplies frequency independence. The weight or weights are applied toeach input signal as either a real-valued Finite Impulse Response (FIR)filter at a chosen intermediate frequency (IF) (as depicted in FIG. 16below) or as complex-valued FIR filter at base band (as depicted in FIG.17 below). Following the application of the appropriate weights, theoutputs from each antenna-channel are summed to yield a beamformedoutput from the array.

[0082]FIG. 16 is a schematic block diagram of a preferred base stationemploying real-valued FIR filtering at IF. In particular, the basestation 1020 employs a sample-data beam shaping system for downconvertedand band limited signals. The mobile unit 30 communicates with the basestation 1020 through a plurality of N receiver units 1010 ₁, 1010 ₂, . .. , 1010 _(N). Each receiver includes a respective antenna 1022 ₁, 1022₂, . . . , 1022 _(N). Received signals are transmitted from the antennas1022 ₁, 1022 ₂, . . . , 1022 _(N) through a bandpass filer, 1024 ₁, 1024₂, . . . , 1024 _(N); a gain controllable amplifier 1026 ₁, 1026 ₂, . .. , 1026 _(N); a multiplier 1028 ₁, 1028 ₂, . . . , 1028 _(N); and asecond bandpass filter 1030 ₁, 1030 ₂, . . . , 1030 _(N) to form Nreceiver output signals.

[0083] The receiver output signals are input to a processing chip 1040which includes a sampling circuit 1042 ₁, 1042 ₂, . . . , 1042 _(N) anda programmable FIR filter 1044 ₁, 1044 ₂, . . . , 1044 _(N) for eachinput signal. The outputs of the FIR filters are summed by a summingcircuit 1046. A postprocessor 1048 communicates with an off-chipautomatic gain control (AGC) circuit 1032 to provide a control signal tothe amplifiers 1026 ₁, 1026 ₂, . . . , 1026 _(N) to vary the amplifiergains.

[0084] The postprocessor 1048 also communicates with an off-chipgeo-location controller 1038 which provides geo-location data to aweighted circuit 1046. The weighting circuit 1036 provides weights tothe on-chip programmable filters 1044 ₁, 1044 ₂, . . . , 1044 _(N).

[0085]FIG. 17 is a schematic block diagram of a preferred base stationemploying complex-valued FIR filtering at base band. As with FIG. 16,the base station 1020′ includes a plurality of receivers that providesan input signal to a processing chip 1050. The processing chip 1050yields two channels of output to an off-chip postprocessor 1034 whichdecodes, encodes and equalizes the channels. The postprocessor 1034transmits a signal to the AGC circuit 1032 to control the receiveramplifiers 1026 ₁, . . . , 1026 _(N) and is in communication with thegeo-location controller 1038. Geo-location data from the geo-locationcontroller 1038 is processed by a weight-update circuit 1036′ tocalculate weights for a 2N M stage FIR filter array.

[0086] The base station includes a beamshaping circuit using a twochannel downconversion system. The processing chip 1050 includes, foreach of N receivers, a sampling circuit 1052 ₁, . . . , 1052 _(N) and amultiplier 1054 ₁, . . . , 1054 _(N). The multipliers 1054 ₁, . . . ,1054 _(N) each provide an in-phase (I) channel 1056 ₁-I, . . . , 1054_(N)-I and a quadrature (2) channel 1056 ₁-Q, . . . , 1056 _(N)-Q. Therespective channels are passed to respective low pass filters 1058 ₁-I,. . . , 1058 _(N)-Q. Each channel is then down-converted bydownconversion circuit 1060 ₁-I, . . . , 1060 _(N)-Q. The down-convertedchannels are fed to respective programmable FIR filters 1062 ₁-I, . . ., 1062 _(N)-Q. These filters are programmed based on the weight inputsfrom the weighting circuit 1038. The I and Q channels are individuallysummed at summing circuits 1064-I, 1064-Q for output to thepostprocessing system 1034.

[0087] The effect of the weights is to electronically shape theantenna-array response. Ideally, mobile transmitters that areinterfering with the desired user are suppressed or nulled out, whilethe transmitter of interest is given at least unity gain. Using a fullyadaptive antenna array, the weights are updated with time as the mobileunit moves or as propagation conditions change. The update of theweights, however, is computationally intensive requiring the computationof the covariance matrix of the array response.

[0088] In comparison, a preferred base station uses position informationobtained from the mobile transmitter (or from the base-station network)to automatically compute the weights to be applied to the input signalsfrom each antenna. As in the fully-adaptive system, the weights areupdated as the mobile transmitter moves. The potential difficulty withthis approach is that it does not explicitly account for changes in thepropagation conditions between the mobile transmitter and the basestation.

[0089] In an effort to characterize the propagation conditions between amobile transmitter and a base station, a series of operations wereperformed using a fully operational digital-TDMA cellular system. Thebase station comprised 6 receiving antennas that can be located witharbitrary spacings. A single, mobile transmitter is used to characterizethe propagation conditions. Based on the signals received at the basestation, profiles of the signal-propagation delay versus time aremathematically computed. Using these results, the worst caseangle-of-arrival is computed. For this case, the delayed signal isassumed to arrive from a reflector along a line perpendicular to a linejoining the base station and the mobile.

[0090] For geo-location-based array-processing to operate, the truelocation of the transmitter is preferably very close to the angle ofarrival (AOA) of the primary propagation path from the mobile.

[0091] When the true location and the AOA of the primary propagationpath differ, the beam pattern produced by geo-location information willnot exactly produce the desired gain and nulling of the mobiles' signal.This condition produces suppression of the undesired mobile's signal,but may not completely cancel or null out the transmission.

[0092] For worst-case propagation conditions, this implies that theelectronically synthesized beam pattern does not provide the optimalgain for receiving this mobile, nor does it completely null out theundesired signals. The difference between the ideal (fully adaptive)array beam pattern and one constructed using only geo-locationinformation is not too great, however, when the true position of themobile and the AOA of the primary propagation path vary by less than afew degrees.

[0093] In practice, the preceding situation occurs when the primarypropagation between the mobile and the base station are notline-of-sight. This often occurs in urban canyons, where large buildingsblock line-of-sight transmission from the mobile to the base station(and vice versa); thereby, placing the mobile's transmission in a “deepfade.” To counteract this effect, a preferred base station includespartially adaptive array-processing to incrementally refine the initialbeam pattern that is obtained using only geo-location information.Candidate approaches for partially-adaptive array processing can bereadily found in the literature for fully-adaptive array processing(e.g., “Novel Adaptive Array Algorithms and Their Impact on CellularSystem Capacity,” by Paul Petrus incorporated herein by reference).

[0094] The approaches to computing a mobile's true location have beeninvestigated in detail for CDMA signal communication (see “Performanceof Hyperbolic Position Location Techniques for Code-Division MultipleAccess,” by George A. Mizusawa, incorporated herein by reference).Implementing a GPS receiver in the phone is one candidate for providingaccurate geo-location information to the base station. Alternatively, atleast three base stations can be employed to triangulate the mobilelocation using a variety of algorithms.

[0095]FIG. 18 is a schematic block diagram of a beamshaping circuitbased on an adaptive-array processing algorithms. As illustrated, thecircuitry 1080 is essentially identical to that illustrated in FIG. 17.The postprocessing circuit, however, communicates with an adaptive-arrayprocessing algorithm in the module 1039 provides the weighting signal tothe on-chip programmable FIR filters 1062 ₁-I, . . . , 1062 _(N)-Q. Theprocessing chip 1050 can be similarly employed to accommodate othercellular communication techniques.

[0096] Although preferred embodiments of the invention have beendescribed in the context of a cellular communication system, theprinciples of the invention can be applied to any communication system.For example, geo-location data and associated beamforming can beembodied in any radio frequency communication system such as satellitecommunication systems. Furthermore, the invention can be embodied inacoustic or optical communication systems.

Equivalents

[0097] While the invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. In particular, the variousaspects of the invention can be embodied in hardware, software orfirmware.

[0098] These and all other equivalents are intended to be encompassed bythe following claims.

[0099] The claims should not be read as limited to the described orderor elements unless stated to that effect. Therefore, all embodimentsthat come within the scope and spirit of the following claims andequivalents thereto are claimed as the invention.

What is claimed:
 1. A communication system comprising: a firsttransceiver located with a first user having a first processor and afirst directional antenna array; a second transceiver located with asecond user having a second processor and a second antenna array; alocator on at least one of the first user and second user thatdetermines a physical location of one of the first and second antennaarray; a spatially multiplexed communication link formed between thefirst and second transceivers, and an adaptive programmable beamformercircuit in the first transceiver that shapes a communication beamdirected between the first antenna array and the second antenna array,the adaptive programmable beamformer circuit having a single integratedchip having a plurality of complex multipliers, a plurality of downconversion circuits and a plurality of finite impulse response (FIR)filters programmable with respect to a plurality of delays and asteering circuit that adjusts the plurality of delays to theprogrammable beamformer circuit.
 2. The system of claim 1 wherein thefirst and second antenna arrays are movable relative to one another andthe programmable beamformer updates the direction of the communicationbeam in response to the relative motion.
 3. The system of claim 1wherein the communication beam is a radio frequency beam.
 4. The systemof claim 1 wherein the locator is responsive to location data from asatellite positioning system.
 5. The system of claim 1 wherein thelocator is responsive to location data from a ground-based positioningsystem.
 6. The system of claim 1 wherein the beamformer includes anulling circuit for suppressing signals outside of the direction of thesecond antenna array.
 7. The system of claim 1 wherein the beamformerincludes an adaptive processing module to alter the shape of thecommunication beam over time.
 8. An acoustic communication systemcomprising: a first transceiver having a directional antenna array, thedirectional antenna array having a first geographical position; a secondtransceiver on a mobile unit having an antenna array, the antenna arraybeing movable relative to the directional antenna array; a spatiallymultiplexed communication link between the first and second transceiversformed by a communication signal between the antenna arrays; apositioning system on the mobile unit that detects a geographicalposition of the mobile antenna arrays, the position of the mobileantenna array being communicated from the mobile transceiver to thefirst transceiver over the communication link; an adaptive programmablebeamformer circuit in the first transceiver that modifies the signal inresponse to the relative motion of the antenna arrays, the adaptiveprogrammable beamformer circuit having a single integrated chip having aplurality of complex multipliers, a plurality of down conversioncircuits and a plurality of finite impulse response (FIR) filtersprogrammable with respect to a plurality of weights and a steeringcircuit that adjusts the plurality of weights to the programmablebeamformer circuit; and a nulling module coupled to the beamformer thatsuppresses interference to the signal.
 9. The system of claim 8 whereinthe beamformer updates the shape of the signal over time.
 10. The systemof claim 8 wherein the signal is a radio frequency beam.
 11. The systemof claim 8 wherein the positioning system is responsive to position datafrom a satellite positioning system.
 12. The system of claim 8 whereinthe positioning system is responsive to position data from aground-based positioning system.
 13. The system of claim 8 wherein thebeamformer includes a plurality of programmable filter arrays.
 14. Thesystem of claim 8 further comprising a table of stored antenna weightsstored in memory, the table accessed by the nulling module to modify thesignal.
 15. The system of claim 8 further comprising an adaptiveprocessing module to alter the shape of the beam over time.
 16. Thesystem of claim 8 wherein the mobile antenna array is a directionalantenna array.
 17. A method for operating an acoustic communicationsystem comprising: operating a first transceiver at a first unit andhaving a first processor and a first directional antenna array;operating a second transceiver on a mobile unit having a secondprocessor and a second antenna array; determining the physical locationof the second antenna array relative to the first antenna array; forminga spatially multiplexed communication link between the first and secondtransceivers, the link including a communication beam between the firstantenna array and the second antenna array; and in an adaptiveprogrammable beamformer integrated circuit chip in the firsttransceiver, responding to the physical location of the second antennaarray, by using a plurality of complex multipliers, a plurality of downconversion circuits and shaping the communication beam using a pluralityof programmable finite impulse response (FIR) filters with respect to aplurality of weights and steering the beam to be directed between thefirst antenna array and the second antenna array using the programmablebeamformer circuit.
 18. The method of claim 17 further comprising thesteps of: moving the first and second antenna arrays relative to oneanother, and in the beamformer, updating the direction of the signalover time in response to the relative movement.
 19. The method of claim17 wherein the communication beam is a radio frequency beam.
 20. Themethod of claim 17 wherein the second transceiver in a mobile unit mayfunction as the first transceiver and the first transceiver may functionas the second transceiver.
 21. The method of claim 17 wherein the stepof determining the physical position is responsive to position data froma satellite positioning system.
 22. The method of claim 17 wherein thestep of determining the physical position is responsive to position datafrom a ground-based positioning system.
 23. The method of claim 17wherein the beamformer includes a nulling circuit to suppress signalsoutside the direction of the second antenna array.
 24. The method ofclaim 17 wherein the beamformer includes an adaptive processing modulefor altering the shape of the communication beam over time.
 25. A methodof operating an acoustic communication system comprising: operating afirst transceiver having a first directional antenna, the firstdirectional antenna having a fixed geographical position; operating amobile transceiver on a mobile unit having a second directional antenna,the second antenna being movable relative to the first directionalantenna; forming a spatially multiplexed communication link between thefirst and mobile transceivers by a communication signal between theantennas; in a positioning system on the mobile unit, detecting thegeographical position of the mobile antenna, the position of the mobileantenna being communicated to the first transceiver over thecommunication link; and in a first adaptive programmable beamformerintegrated circuit chip in the first transceiver and a secondprogrammable beamformer integrated circuit chip in the mobiletransceiver, modifying the signal in response to the relative motion ofthe antennas by using a plurality of complex multipliers, a plurality ofdown conversion circuits and shaping the communication signal using aplurality of finite impulse response (FIR) filters programmable withrespect to a plurality of weights, and steering a beamformed signal. 26.The method of claim 25 wherein the step of modifying the signalcomprises updating the direction of the signal over time in response tothe relative movement of the antennas.
 27. The method of claim 25wherein the step of modifying comprises determining the range betweenthe first antenna and the mobile antenna and, when the range is lessthan a specific range, modifying the signal to be omnidirectional. 28.The method of claim 25 wherein the signal is a radio frequency beam. 29.The method of claim 25 wherein the step of detecting comprises receivingposition data from a satellite positioning system.
 30. The method ofclaim 25 wherein the step of detecting comprises receiving position datafrom a ground-based positioning system.
 31. The method of claim 25wherein the beamformers include a plurality of programmable filterarrays.
 32. The method of claim 25 wherein the step of modifying thesignal comprises providing antenna weights from a table stored inmemory.
 33. The method of claim 25 wherein the step of modifying thesignal comprises performing adaptive processing to alter the shape ofthe signal over time.
 34. The method of claim 25 wherein the step ofmodifying the signal comprises suppressing interference with the signalin a nulling module.
 35. The method of claim 25 wherein the step offorming the communication link comprises a spatially multiplexed signal.36. A beamforming circuit for an acoustic communication systemcomprising: a plurality of sampling circuits for receiving communicationsignals; a plurality of programmable finite impulse response (FIR)filters, each FIR filter being connected to a sampling circuit; asumming circuit that sums filtered signals from the plurality of FIRfilters; and a directional communication signal formed from the summedsignals.
 37. The circuit of claim 36 wherein the sampling circuits, theplurality of programmable FIR filters and the summing circuit are formedon a single integrated circuit.
 38. The circuit of claim 36 furthercomprising a multiplier connected to each sampling circuit to generatean in-phase channel and a quadrature channel, each channel beingconnected to a filter, a converter and one of the FIR filters.
 39. Thecircuit of claim 36 wherein the communication system comprises anacoustic network including a plurality of transceivers that communicateby a communication link with mobile transceiver units, and furtherincluding a unit having an adaptive array processor providing weightingsignals to the FIR filters.